Director system for broadband antennas



March 10, 1970 F, SAUL, 5R ET AL 3,500,425

DIRECTOR SYSTEM FOR BROADBAND ANTENNAS Filed 001;. so, 1967 mnllllllll Illl INVENTORS F. KENNETH SAUL SR. Eowm A. ADAMS ATTORNEYS.

United States Patent 3,500,425 DIRECTOR SYSTEM FOR BROADBAND ANTENNAS Francis Kenneth Saul, Sr., Delhi, Ontario, and Edwin A.

Adams, Simcoe, Ontario, Canada, assignors to Delhi Metal Products Limited, Delhi, Ontario, Canada Filed Oct. 30, 1967, Ser. No. 678,948 Claims priority, applicatio6n Canada, Sept. 20, 1967, 5 8

Int. Cl. H01q 21/00 US. Cl. 343--817 4 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of the invention This invention relates particularly to VHF television antennas although it could find applications in VHF antennas, and in particular to an improved VHF director element and antennas incorporating such director elements.

Description of the prior art The increasing popularity of television and FM broadcasting programs has created a considerable demand for television antennas that enable relatively good reception on all television high-band and low-band channels as well as on the FM frequency band in remote areas from the broadcasting antennas, commonly referred to as fringe areas. Recent developments have produced a variety of high-gain wide-band antennas which can provide relatively high gain on low-band and high-band channels, that is, channels 2 to 6 (54 to 88 megacycles) and channels 7 to 13 (174 to 216 megacycles).

In order to improve the gain and directivity characteristics of VHF antennas which generally comprise an array of dipole elements of different lengths, it is known to provide one or more passive elements namely directors which are disposed in front of the active elements (dipole elements), and reflectors behind the active elements. The are of parasitic director elements is relatively well developed, and examples of modern multiband parasites are illustrated in United States Reissue Patent No. 25,437 to Henderson, dated Aug. 27, 1963, and in United States Patent No. 3,277,491 which issued on Oct. 4, 1966, on an invention by Charles C. Liu.

These references teach the use of director elements of particular configurations wherein main sections constitute resonating low-band and F M frequency band components, and wherein auxiliary elements are mounted on the main sections and cooperate therewith to provide high-band resonators. While antennas using such director elements have exhibited good electromagnetic properties, they are necessarily large and of complex configurations on account of the large number of passive elements required and, as a result, such antennas are comparatively costly and generally suffer from lack of structural rigidity.

SUMMARY OF THE INVENTION We have discovered that satisfactory electromagnetic properties can be achieved with fewer director elements and hence antennas having better structural rigidity are feasible wherein, in accordance with this invention each director element comprises a main section defining three high-band resonating structures electrically insulated one from the other and disposed in an end to end relationship, and two extension means each electrically connected to a different one of the outer high-band resonating structures and co-operating therewith to provide a low-band and FM frequency band resonating structure.

The invention therefore, provides an improved director element for use in combination with active elements in a broadband television antenna system, which director element comprises an elongated straight rigid member adapted to be disposed transversely of the direction of electromagnetic wave propagation in a plane parallel to the plane of signal polarisation and consisting of three high-band frequency parasitic sections electrically insulated one from another; and two conductive generally L-shaped members disposed in a vertical plane that contains said straight member and each associated with a different one of the outer high-band frequency parasitic sections, one leg of each L-shaped member being generally parallel and conductively coupled to the intermediate portion of the associated high-band section by means of the other leg which is generally vertical, and said one leg projecting inwardly therefrom so as thereby to cooperate with the outer portion of said associated high-band section and define a low-band and FM band frequency parasitic section. In a preferred embodiment in accordance with the invention the inner ends of said one leg of said L-shaped members, which are parallel to the high-band sections are mechanically interconnected to one another by means of an electrically insulating member.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be further described with reference to the accompnaying drawings in which:

FIGURE 1 is a perspective view of a five active element antenna system incorporating three director elements in accordance with this invention,

FIGURE 2 is an enlarged detailed front view of one of the director elements seen in FIGURE 1, and

FIGURE 3 is a front view of one side of the element illustrated in FIGURE 2 with a voltage curve illustrating the modes of operation at low-band frequencies.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The antenna system illustrated in FIGURE 1 and referred to generally by reference numeral 10 comprises an array 11 of active elements and a group 12 of passive elements, all of which are rigidly secured to a boom or cross member 13 which in turn is adapted to be connected to an antenna mast 14 as at 15.

The array 11 of active elements consists of a number (five in the illustrated embodiment) of dipole elements 16A to 16E of decreasing lengths, dipole element 16E being the shortest one, interconnected in known manner by a transposed harness 17 to signal leads 18. This type of TV antenna is well known in the art for its relatively good electromagnetic radiation characteristics on low and high-band frequencies, i.e., channels 2 to 6 and 7 to 13 respectively, but it alone cannot provide the very high gain required for fringe area reception.

It is known to provide passive elements in order to increase the gain and directivity of VHF antennas, and as mentioned hereinbefore this invention provides an improved director element which can be substituted advantageously for director elements of prior designs. As will be apparent to those skilled in the art, the range of application of director elements in accordance with this invention is not limited to TV antennas of the above mentioned type, it being understood that this particular TV antenna is mentioned herein on account of its present popularity.

The group 12 of passive elements disposed ahead of the shorter dipole element 16E consists of a number of progressively shorter director elements 19A, 19B and 19C. Each director element 19A, 19B, 19C comprises an elongated straight rigid member 20A, 20B, 20C horizontally disposed and transverse to the direction of electromagnetic radiation propagation, and two conductive generally L- shaped members 21A, 22A; 21B; 22B; and 21C, 22C.

As best illustrated in FIGURE 2, the straight rigid member 20 of director element 19 consists of three conductive rods 25, 26, 27 horizontally disposed and mechanically held together by electrical insulating elements 28 and 29 in an end-to-end relationship. These rods 25, 26, 27, by virtue of their electrical lengths with respect to the highband frequency range, define three high-band parasitic sections.

Each L-shaped member 21, 22 has horizontal legs 31, 32 conductively coupled to the intermediate portion of a different one of the outer high-band sections 25, 27 by means of the other generally vertical legs 41, 42. The horizontal legs 31, 32 project inwardly towards one another and co-operate with the outer portions 35, 37 of the associated high-band sections 25, 27 to define two low-band and FM frequency parasitic sections. Although the horizontal legs 31 and 32 are disposed below the rigid member 20, it should be apparent that they could also be disposed above the high-band rods 25, 26, 27.

Thus, each director element 19A, 19B, 19C presents a set of three parasitic sections 25, 26 and 27 approximately equal to one half wavelength of a particular range of frequencies within the high-band frequency limits, i.e., 174

and 215 megacycles per second, and two parasitic sections each made up of a horizontal leg 31, 32 of one of the L- shaped member 21, 22 and an outer portion 36, 37 of one of the two outer high-band parasitic sections 25, 27 for a combined electrical length corresponding to approximately one half wavelength of a particular range of frequencies within the lower limit of low-band frequencies (54 megacycles per second) and the upper FM band frequency, namely 108 megacycles per second.

In FIGURE 2, the resonant voltage distribution on the high-band sections 25, 26, 27 is illustrated by voltage curves 55, 56, 57 from which it can be seen that the signal voltages are minimum at points 55A, 56A, 57A and maximum at insulators 28, 29, i.e., at both ends of each parastic sections 25, 26, 27 The signal voltage distribution for the low-band and FM frequency sections extends likewise over the length of the sections with points of maximum voltages at the ends and a point of minimum voltage approximately equidistant from the ends. However, the low-band and FM frequency sections being composite elements the signal voltage distribution has a discontinuity at the junction of the L-shaped members 21, 22 and the associated outer high-band sections 25, 27. This can be seen at 61 on the signal voltage curve 60 shown in FIGURE 2, but the resultant distribution could be illustrated by the expanded curve 62 shown in FIGURE 3 with a null spot at 63.

By this arrangement, the point 63 of null voltage on curve 62 being out of the critical areas of maximum voltages on the outer high-band sections 25, 27 and provided the auxiliary members 21, 22 are sufficiently far from these critical areas, which is accomplished here by disposing the horizontal legs 31, 32 of L-shaped members 21, 22 a short distance from the adjacent high-band sections 25, 27, the presence of such generally L-shaped auxiliary members 21, 22 does not interfere with the resonance of said high-band sections 25, 27 when electromagnetic radiation of the resonant frequencies are encountered.

The inner end of horizontal legs 31 and 32 may be mechanically interconnected by an electrically insulating member 70 which in turn may be rigidly secured to the straight member 20 or to the support boom 13 by a small support 71.

Although in the accompanying drawings the antenna includes three director elements in combination with five active elements, it should be understood that the invention is not limited to any particular number of director elements, and in fact only one may sometimes be used with one or more active elements. Moreover, legs 41, 42 of the generally L-shaped members 21, 22, which appear in the drawings as straight members could be made slightly -arcuate if desired and do not have to be exactly vertical as shown for satisfactory operation.

We claim:

1. A TV antenna director element comprising an elongated straight rigid member adapted to be disposed transversely of the direction of electromagnetic wave propagation in a plane parallel to the TV signal polarisation plane and consisting of three high-band frequency parasitic sections electrically insulated one from another; and two conductive generally L-shaped members disposed in a vertical plane that contains said straight member and each associated with a different one of the outer high-band frequency parasitic sections, one leg of each L-shaped member being generally parallel and conductively coupled to the intermediate portion of the associated high-band section by means of the other leg which is generally vertical, and said one leg projecting inwardly therefrom so as thereby to cooperate with the outer portion of said associated high-band section and define a low-band and FM-band frequency parasitic section.

2. A director element as defined in claim 1 wherein the inner ends of said one leg of said generally L-shaped members are mechanically interconnected by electrically insulating support means.

3. An antenna system adapted for TV signals on high and low frequency bands as well as FM frequencies, having in combination one or more active elements and at least one director element mounted on a support boom,

characterized in that said director element comprises an elongated straight rigid member adapted to be disposed transversely of the direction of electromagnetic wave propagation in a plane parallel to the plane of TV signal polarisation and consisting of three high-band frequency parasitic sections electrically insulated one from another; and two conductive generally L-shaped members disposed in a vertical plane that contains said straight member and each associated with a different one of the outer high-band frequency parasitic sections, one leg of each L-shaped member being generally parallel and conductively coupled to the intermediate portion of the associated high-band section by means of the other leg which is generally vertical, and said one leg projecting inwardly therefrom so as thereby to co-operate with the outer portion of said associated high-band section and define a low-band and FM band frequency parasitic section.

4. An antenna system as defined in claim 3 wherein the inner ends of said one leg of said L-shaped members are mechanically interconnected by electrically insulating support means.

References Cited UNITED STATES PATENTS 2,821,711 1/1958 Lo 343800 X 2,897,497 7/1959 Finneburgh 343-815 ELI LIEBERMAN, Primary Examiner M. NUSSBAUM, Assistant Examiner U.S. Cl. X.R. 3438l8, 833 

